Funky Leaf Spot, Viruses, and Xylella Update Winter Phillip M. Brannen University of Georgia Plant Pathology Department

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1 Funky Leaf Spot, Viruses, and Xylella Update Winter 2011 Phillip M. Brannen University of Georgia Plant Pathology Department

2 Background: Systemic Blueberry Diseases At least nine species of plant viruses infect blueberries in North America Some (such as scorch and shock viruses) are very damaging, whereas most others are highly variable in level of damage Historically, southern blueberries have been essentially virus-free 2000: a few plants positive for Blueberry shoestring virus or Strawberry latent ringspot virus in south GA 2001: no positives in sample of 93 suspects in large NC & GA virus survey Since 2005: increased prevalence and severity of viral and virus-like diseases on southern highbush

3 Blueberry red ringspot virus (BRRV) Fall Spring

4 Blueberry red ringspot virus (BRRV) BRRV on Ozarkblue fruit in NC (courtesy Bill Cline, NCSU) Mosaic, mottling, ringspotting Foliar symptoms most pronounced in fall (absent in spring) Stem symptoms most pronounced in spring Fruit symptoms not seen in GA No known in-field vector, most likely transmitted via cuttings Effects on plant growth and yield poorly documented

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7 Prevalence of Blueberry red ringspot virus (BRRV) and necrotic ringspot disease in different counties in Georgia, based on a survey conducted in fall of Scherm et al., 2008

8 Prevalence of Blueberry red ringspot virus (BRRV) and necrotic ringspot disease on different southern highbush cultivars in Georgia, based on a survey conducted in fall of Scherm et al., 2008

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10 Phil Harmon (Univ. of Florida) did observe transmission of the disease in a greenhouse. Infected plants on one table, collected for experimentation, were placed opposite non-infected plants. Within two months, most of the non-infected plants were showing the disease symptoms. Mites were found in association with the diseased plants, but data is preliminary at best.

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12 Blueberry Shock Spread through propagation or pollen (bees). In theory, the bees coming from Michigan to Georgia should not be a problem, since the pollen would not be active when the bees come to Georgia (pollen too old). 1-2 year latent period before symptoms. Plants eventually recover, but losses are severe for several years.

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14 Blueberry Scorch Spread through propagation or aphids. 1-2 year latent period before symptoms. Plants eventually die, and losses are significant until death occurs.

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19 A small, fastidious, Gram negative, xylem-inhabiting bacterium related to Xanthomonas spp. Tissue specific, confined to tracheary elements, tracheids or vessels Xylella fastidiosa Temecula isolate (WT)) Photo by H.C. Hoch, Cornell University; Journal of Bacteriology. 189:

20 XF1968F3/XF1968R3 Primer Results Results from multiple primers indicate the blueberry X. fastidiosa is not piercei 1 kb BB21 BB1 BB9 G11 Teme OL2 T1B T5C Dixon M12 FL GA Neg Ladder Oak Plum Ctrl Blueberry Grape Oleander Almond Several strains of X. fastidiosa courtesy of Dr. Jianchi Chen, USDA-ARS, Parlier, CA L. Nissen and T. Denny

21 Blueberry survey locations with confirmed Xylella fastidiosa infections. Plants symptomatic for bacterial leaf scorch were confirmed through ELISA (map developed using Google Earth).

22 Incidence (percentage of symptomatic plants) of bacterial leaf scorch by cultivar at one 7th leaf producer site in Colquitt County. The number of rows surveyed (n) is shown in parentheses next to the cultivar name.

23 Emerald FL [V1] Millennium Windsor Southern Belle

24 Disease incidence (%) FL (V1) y = x R 2 = F = Disease incidence (%) Star y = x R 2 = F = Years Years Disease incidence (percentage of symptomatic plants) of bacterial leaf scorch observed on cultivars FL (V1) and Star over time (years in the field). Both cultivars are susceptible to the disease, but FL is clearly more susceptible to disease development and spread than Star. Based on the trend lines projected through use of survey data, ~75% of FL plants would be symptomatic by the tenth year in the field, versus ~30% in Star.

25 Can we screen for resistance in the greenhouse to obtain rapid evaluations of blueberry lines?

26 Blueberry leaf scorch symptom Development with 10-fold dilution of 0.25 OD BB08-2 Inoculum (2009) V1 Star Windsor Emerald wk 8 wk 10 wk 12 wk 14 wk 16 wk 18 wk

27 Blueberry leaf scorch symptom development with 0.25 OD BB08-3 inoculum (2010 test) 4 3 V1 Star Windsor Emerald mo 3 mo 4 mo 5mo

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31 Blueberry leaf scorch symptom development with 0.25 OD BB08-3 inoculum (2010 test) 4 3 V1 Climax Southern Belle Tif Blue Rebel mo 3 mo 4 mo 5 mo

32 Comparison of Field Resistance to Blueberry Leaf Scorch and Greenhouse Resistance Cultivar Field Greenhouse V1 Susceptible Susceptible Star Susceptible Moderate Res. Windsor Resistant Resistant Emerald Resistant Susceptible Rebel Susceptible Susceptible Southern Belle Resistant Resistant Climax? Resistant Tif Blue? Resistant

33 Pathogenicity of Xylella fastidiosa strains to Emerald, 2010 test Leaf scorch rating BB08-3 EB06-1SC BB08-1 B1-10 GA B2-64 GA B2-66 GA Buffer 0 Four months after Inoculation

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35 Greenhouse Screening for Resistance to Leaf Scorch Resistance to blueberry leaf scorch in greenhouse screening agreed with observed field resistance for most cultivars. Emerald was more susceptible to Xylella fastidiosa in the greenhouse than in the field. Star appeared to be more resistant in greenhouse tests than has been observed in the field. Differences between greenhouse and field observations could be due to host specificity of strains, aggressiveness of strains, or loss of virulence in some strains during culture.

36 Evaluation of Benign Strains of X. fastidiosa for the Biological Control of Blueberry Leaf Scorch by Cross-Protection Various strains of X. fastidiosa are being evaluated in the greenhouse for biological control of blueberry leaf scorch in Star and V1, including strains from elderberry, blackberry, sycamore, and mulberry. Star and V1 blueberry plants inoculated with these strains were challenged 3-4 weeks later with the blueberry leaf scorch strain BB08-2 in 2009 or BB08-3 in 2010 to evaluate biological control of the disease. Disease incidence and severity are rated once a month. Don Hopkins, UF

37 Biological Control of Blueberry Leaf Scorch in V1 (2010 test) 3 Buffer EB92-1 Syc86-1 BKB95-1 Leaf scorch rating 2 1 Dixon PD Five months after Inoculation with BB08-3

38 Biocontrol of Blueberry Leaf Scorch In greenhouse tests, X. fastidiosa strains EB92-1 and Syc86-1 reduced leaf scorch in both Star and V1. BKB95-1 provided biocontrol in Star and PD00-2 was effective in V1. Strain PD00-2 is not a candidate for biocontrol of blueberry leaf scorch, because it is pathogenic to grapevine. Further greenhouse and field tests are warranted for EB92-1, Syc86-1, and possibly BKB95-1.

39 Summary In addition to X. fastidiosa strains from blueberry, strains from lupine, almond, and elderberry were pathogenic to blueberry. Resistance to blueberry leaf scorch in greenhouse screening agreed with observed field resistance for most cultivars. The development of a quick screening test for resistance to leaf scorch is possible. Differences in virulence or host specificity were observed in X. fastidiosa strains used in greenhouse tests. Greenhouse tests for the biological control of leaf scorch were positive. Field tests are needed.

40 Vectors of Xylella species diseases are limited to sharpshooter and spittlebug insects, of which the glassy-winged sharpshooter (Homalodisca vitripennis) is primary in the Southeast. University of California

41 Emphasis on glassy-winged sharpshooter (Homalodisca vitipennis), which constituted 97% of leafhoppers sampled within bushes season-long at two field sites 97% Credit: University of California 0.25% 0.77% 0.25% 1% Credits: Susan Ellis Homalodisca insolita Paraulacizes irrorata Oncometopia nigricans Draeculacephala spp Graphocephala versuta 0.51% Dr. Moukaram Tertuliano, 2009

42 Feeding preference of glassy-winged sharpshooter in choice test 27% 17% 55% Emerald Star V1 Total of 4 plants (reps) per cultivar tested sequentially For each rep, 20 leafhoppers released in cage containing one plant per cultivar Five days observation, plant position rotated every day Number of leafhoppers settled/feeding per plant recorded daily GWSS feeding on blueberry cultivar

43 Early plant growth (3 months after transplanting) was reduced for BRRV and Xylella cuttings, although Xylella cuttings were still asymptomatic at that time. In fall 2010, 15 months after transplanting, 100, 8.9 and 0% of plants derived from the summer 2009 BRRV, Xylella, and funky spot cuttings, respectively, showed visual disease symptoms. Scherm et al., 2010

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